package com.lagou.sqlSession;

import com.lagou.pojo.BoundSql;
import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.utils.GenericTokenParser;
import com.lagou.utils.ParameterMapping;
import com.lagou.utils.ParameterMappingTokenHandler;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;

public class SimpleExecutor implements Executor{

    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        //1. 注册驱动，获取连接
        Connection connection = configuration.getDataSource().getConnection();

        // 2. 获取sql : select * from user where = #{id} and username = #{username}
            // 转换sql : select * from user where id = ? and username = ?，转换过程中，需要对括号中值存储
        String sql = mappedStatement.getSqlString();
        BoundSql boundSql = getBoundSql(sql);

        // 3.获取预处理对象 preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4. 设置参数

        String parameterType = mappedStatement.getParameterType();
        Class<?> parameterTypeClass = getClassType(parameterType);


        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();

            // 反射
            Field declaredField = parameterTypeClass.getDeclaredField(content);
            // 暴力访问
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[i]);

            preparedStatement.setObject(i+1,o);
        }

        // 5. 执行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);
        Object o = resultTypeClass.getDeclaredConstructor().newInstance();
        ArrayList<Object> objects = new ArrayList<Object>();


        // 6. 获取结果集
        while (resultSet.next()) {
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i < metaData.getColumnCount(); i++) {
                // 获取字段名
                String columnName = metaData.getColumnName(i);
                // 字段值
                Object value = resultSet.getObject(columnName);
                // 使用反射，根据数据库表和实体对应关系完成封装
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();

                // 如何实现的 绑定参数
                writeMethod.invoke(o,value);
            }
            objects.add(o);
        }
        
        
        return (List<E>) objects;
    }

    private Class<?> getClassType(String parameterType) throws ClassNotFoundException {
        if(parameterType != null){
            Class<?> aClass = Class.forName(parameterType);
            return aClass;
        }
        return null;
    }

    /**
     * 完成对#{} 解析工作：
     *  1. 将#{}用？代替，
     *  2. 解析出#{}里的值进行存储
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql){
        // 标记处理类：配置标记解析器来完成对定位符的解析处理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        // 解析后sql
        String parseSql = genericTokenParser.parse(sql);
        // #{} 中参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();
        BoundSql boundSql = new BoundSql(parseSql,parameterMappings);


        return boundSql;
    }
}
